/*
 * Copyright (c) 2011 Adrian Sai-wah Tam
 * Copyright (c) 2015 ResiliNets, ITTC, University of Kansas
 *
 * SPDX-License-Identifier: GPL-2.0-only
 *
 * Original Author: Adrian Sai-wah Tam <adrian.sw.tam@gmail.com>
 * Documentation, test cases: Truc Anh N. Nguyen   <annguyen@ittc.ku.edu>
 *                            ResiliNets Research Group   https://resilinets.org/
 *                            The University of Kansas
 *                            James P.G. Sterbenz <jpgs@ittc.ku.edu>, director
 */

#ifndef TCP_OPTION_SACK_H
#define TCP_OPTION_SACK_H

#include "tcp-option.h"

#include "ns3/sequence-number.h"

namespace ns3
{

/**
 * @brief Defines the TCP option of kind 5 (selective acknowledgment option) as
 * in \RFC{2018}
 *
 * TCP SACK Option is used by a receiver to report non-contiguous blocks of data
 * that have been received and queued in the receiving buffer. Using the
 * information conveyed in SACK option sender retransmits only the segments that
 * have actually been lost, allowing the recovery of multiple packet losses per
 * sending window.
 *
 * Each SACK block is defined by two 32-bit unsigned integers specifying the
 * left and the right edge of the block. It means that with the 40-byte TCP
 * option limitation in addition to the presence of TCP Timestamp Option, the
 * maximum number of SACK blocks that can be appended to each segment is 3.
 */
class TcpOptionSack : public TcpOption
{
  public:
    /**
     * @brief Get the type ID.
     * @return the object TypeId
     */
    static TypeId GetTypeId();
    TypeId GetInstanceTypeId() const override;

    typedef std::pair<SequenceNumber32, SequenceNumber32> SackBlock; //!< SACK block definition
    typedef std::list<SackBlock> SackList;                           //!< SACK list definition

    TcpOptionSack();
    ~TcpOptionSack() override;

    void Print(std::ostream& os) const override;
    void Serialize(Buffer::Iterator start) const override;
    uint32_t Deserialize(Buffer::Iterator start) override;

    uint8_t GetKind() const override;
    uint32_t GetSerializedSize() const override;

    /**
     * @brief Add a SACK block
     * @param s the SACK block to be added
     */
    void AddSackBlock(SackBlock s);

    /**
     * @brief Count the total number of SACK blocks
     * @return the total number of SACK blocks
     */
    uint32_t GetNumSackBlocks() const;

    /**
     * @brief Clear the SACK list
     */
    void ClearSackList();

    /**
     * @brief Get the SACK list
     * @return the SACK list
     */
    SackList GetSackList() const;

    friend std::ostream& operator<<(std::ostream& os, const TcpOptionSack& sackOption);

  protected:
    SackList m_sackList; //!< the list of SACK blocks
};

/**
 * @brief Output operator.
 * @param os The output stream.
 * @param sackOption the option to print.
 * @returns The output stream.
 */
std::ostream& operator<<(std::ostream& os, const TcpOptionSack& sackOption);

/**
 * @brief Output operator.
 * @param os The output stream.
 * @param sackBlock the block to print.
 * @returns The output stream.
 */
std::ostream& operator<<(std::ostream& os, const TcpOptionSack::SackBlock& sackBlock);

} // namespace ns3

#endif /* TCP_OPTION_SACK */
